The present invention relates generally to a geothermal direct exchange (“DX”) heating/cooling system, which is also commonly referred to as a “direct expansion” heating/cooling system, comprising various design improvements and various specialty applications. More specifically, the present invention pertains to novel designs for encasements used to install refrigerant tubing in a vertical well DX heating/cooling system.
Geothermal ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged fluid transport tubing. The tubing loop is extended to the surface and is then used to circulate either the naturally warmed or the naturally cooled fluid to an interior air heat exchange means.
Geothermal water-source heating/cooling systems of a traditional design typically circulate, via a water pump, a fluid comprised of water, or water with anti-freeze, in plastic (typically polyethylene) underground geothermal tubing so as to transfer geothermal heat to or from the ground in a first heat exchange step. In a second heat exchange step, a refrigerant heat pump system is utilized to transfer heat to or from the water. In a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) is utilized to transfer heat to or from the refrigerant to heat or cool interior air space.
In more contemporary geothermal DX heat exchange systems, the refrigerant fluid transport lines are placed directly in the sub-surface ground and/or water. The fluid transport lines typically circulate a refrigerant fluid, such as R-22, R-410A, or the like, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer geothermal heat to or from the sub-surface elements via a first heat exchange step. DX systems require only a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems are generally more efficient than water-source systems because fewer heat exchange steps are required and because no water pump energy expenditure is necessary. Further, DX systems are generally more efficient than water-source systems because copper is a better heat conductor than most plastics, and because the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system. Also, less excavation and drilling are typically required, and installation costs are typically lower, with a DX system as compared to a water-source system.
While most in-ground/in-water DX heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.
The present invention primarily relates to DX systems installed with vertically oriented sub-surface geothermal heat exchange apparatus, although an embodiment to utilize the invention in a lake or similar installation is also disclosed. Historically, copper refrigerant transport tubing is inserted within vertically oriented wells/boreholes by dropping and/or pushing the copper tubing into the wells. Several problems are encountered with this procedure. First, the refrigerant transport tubing is generally comprised of one smaller sized liquid copper refrigerant transport tube and one larger sized copper vapor refrigerant transport tube, coupled by means of a U-bend, or the like, at or near the lower distal end of the refrigerant transport tubing within the well. The lower distal end of the refrigerant transport tubing is subject to bending and/or other damage as it is lowered into the well and when it comes into contact with the bottom of the well. For example, the U-bend can be scraped, dented, punctured, or crimped. Any such damage can either impede the refrigerant flow and impair system operational efficiencies or create a refrigerant leak which renders the system totally useless.
Further, those of skill in the art understand that when refrigerant tubing is installed within a well, several other problems can periodically be encountered. One such problem is that casing is sometimes required to shore up-loose soil until solid rock is encountered. In such case, a smaller drill bit is extended through the casing and is then used to drill through the rock to the desired depth. As a result, a small, rounded ledge of rock is usually left at the point within the well where the casing stops and the drilling through the rock begins. This occurs because the smaller drill bit used to drill through the rock has a smaller diameter than the larger drill bit used to open a hole large enough for the casing. Casing, for example, may be 6 inches in diameter, whereas the drill bit through the lower rock may be only 4.5 inches in diameter. This small rock ledge quite often acts as an impediment to lowering the copper refrigerant transport lines into the well.
This small rock ledge also quite often acts as an impediment to lowering the trimmie tube into the well. A trimmie tube is used to pump grout into the well from the bottom to the top, so as to remove all air gaps once the copper tubing has been installed. A trimmie tube is often a 1 to 1.25 inch diameter polyethylene tube, or the like, with a round, open, distal end. The trimmie tube must be installed together with the copper tubing all the way to, or near, the bottom of the well. Often, even if the trimmie tube is able to be worked past a rock ledge by pushing, pulling, and twisting, the distal end of the tubing is damaged to the extent that the insertion of grout through the tube is impaired or even blocked.
Because trimmie tubes are generally stored in a coiled fashion, as are most soft copper refrigerant grade tubes, the “memory” of the plastic tube coil when it is being lowered into a confined, straight, and vertically oriented walled borehole/well causes the tubing to push against the interior walls of at least one of the casing and the rock well. Such abrasion is wearing on the tubing, and results in additional force being required in an effort to push the tubing down into the well from the top. Simultaneous pushing on soft copper tubing usually results in additional tubing abrasion, occasioned by the walls of the well, and increases the danger of kinking or otherwise damaging the copper tubing.
A third problem is that naturally occurring underground water is sometimes encountered within a well/borehole. While copper tubing is generally heavier than water, when the liquid refrigerant transport tube is insulated, the added displacement of the insulation results in flotation. This can require one to forcibly push the copper tubing, including the insulated liquid line, into the well in order to get it to the design depth at the bottom. Further, so as to prevent the copper tubing with an insulated liquid line from floating out of the well, the installer must secure the copper tubing at the top of the well.
A fourth problem encountered with a DX system, when an insulated liquid line is utilized, is that the insulation surrounding the liquid line displaces enough grout (Grout 111 is over twice the weight of water) so as to cause the copper tubing to float out of the well when the grout fill material is pumped in. This is a bothersome concern requiring the installer, as in the case of a well filled with water, to block, to tie down, or to otherwise secure the top of the copper tubing extending from the top of the well, at least until the grout cures if a cementitious grout, such as Grout 111 or the like, is utilized. Grout 111 is a shrink/crack resistant cementitious grout that is highly water impermeable that was developed by Brookhaven National Laboratory in New York and is well understood by those skilled in the art.
A fifth problem periodically encountered when installing DX system geothermal refrigerant transport tubing within a vertically oriented well/borehole is that rocks, particularly if shale or the like, can slide across the borehole, thereby impeding tubing installation. Efforts to eliminate such impediments were generally limited to either re-drilling and/or cleaning out the borehole, or to dropping a heavy steel bar, secured to the surface by a rope, into the hole in an effort to break through the barrier. These conventional methods required significant extra time and labor.
Consequently, a method is needed for efficiently and safely installing copper tubing, particularly when at least one of the refrigerant transport lines is insulated. Also needed is a method for efficiently and safely installing the trimmie tube to be used for grouting, so as to avoid the problems of tubing damage, abrasion, blocking rocks/ledges/rims, and flotation.